TypeScript Interview Questions and Answers

TypeScript is a language that aims at easing development of large scale applications written in JavaScript. TypeScript adds common concepts such as classes, modules, interfaces, generics and (optional) static typing to JavaScript. It is a superset of JavaScript: all JavaScript code is valid TypeScript code so it can be added seamlessly to any project. The TypeScript compiler emits JavaScript.

TypeScript is a superset of the JavaScript language. It differentiates itself from competitors like CoffeeScript and Dart in that plain JavaScript code can be intermixed with TypeScript. Therefore, JavaScript is TypeScript. But TypeScript has to be compiled into JavaScript before it can run in any JavaScript engine (web browser or node.js). This means you cannot embed TypeScript into a web page directly using <script> tags, but TypeScript (in .TS files) can get compiled into JavaScript (in .JS files) for usage.

TypeScript supports definition files that can contain type information of existing JavaScript libraries, much like C++ header files can describe the structure of existing object files. This enables other programs to use the values defined in the files as if they were statically typed TypeScript entities. There are third-party header files for popular libraries such as jQuery, MongoDB, and D3.js. TypeScript headers for the Node.js basic modules are also available, allowing development of Node.js programs within TypeScript.

First public version released in 2012 (TypeScript 0.8)

TypeScript 0.9 released in 2013, adding support for generics

TypeScript 1.0 released in 2014, including support baked into Visual Studio

Typescript is a strongly typed, object oriented, compiled language. Typescript is a superset of JavaScript that brings users optional static types and solid tooling. Using TypeScript can help avoid painful bugs people commonly run into when writing JavaScript by type checking the code. It was designed by Anders Hejlsberg (designer of C#) at Microsoft. TypeScript is both a language and a set of tools. TypeScript is a typed superset of JavaScript compiled to JavaScript. In other words, TypeScript is JavaScript plus some additional features.

TypeScript is a JavaScript: TypeScript starts with JavaScript and ends with JavaScript. Typescript adopts the basic building blocks of your program from JavaScript. Hence, you only need to know JavaScript to use TypeScript. All TypeScript code is converted into its JavaScript equivalent for the purpose of execution.

TypeScript supports other JS libraries: Compiled TypeScript can be consumed from any JavaScript code. TypeScript-generated JavaScript can reuse all of the existing JavaScript frameworks, tools, and libraries.

JavaScript is TypeScript: This means that any valid .js file can be renamed to .ts and compiled with other TypeScript files. JavaScript is not suitable for developing large applications because of the complexity of large applications. Typescript allows the developers to develop large applications by using object-oriented principles.

TypeScript is portable: Typescript is portable across browsers, devices, and operating systems. It can run on any environment that JavaScript runs on. Unlike its counterparts, TypeScript doesn’t need a dedicated VM or a specific runtime environment to execute.

TypeScript and ECMAScript: TypeScript language features like Modules and class-based orientation are in line with the EcmaScript 6 specification.

TypeScript Language: The most important part for developers is the new language. The language consists of new syntax, keywords and allows you to write TypeScript.

TypeScript Compiler: The TypeScript compiler is open source, cross-platform and open specification, and is written in TypeScript. Compiler will compile your TypeScript into JavaScript. And it will also emit error, if any. It can also help in concatenating different files to a single output file and in generating source maps.

TypeScript Language Service: The “Language Service” exposes an additional layer around the core compiler pipeline that are editor-like applications. The language service supports the common set of a typical editor operations like statement completions, signature help, code formatting and outlining, colorization, etc. TypeScript language service which powers the interactive TypeScript experience in Visual Studio, VS Code, Sublime, the TypeScript playground and other editor.

It’s quite possible that JavaScript libraries/frameworks don’t have TypeScript definition files and yet you want to use them without any errors. The solution is to use the declare keyword. The declare keyword is used for ambient declarations where you want to define a variable that may not have originated from a TypeScript file.

YES. There are 4 main principles to Object Oriented Programming: Encapsulation, Inheritance, Abstraction, and Polymorphism. TypeScript can implement all four of them with its smaller and cleaner syntax.

The module system is an interesting feature of TypeScript, the statically typed superset of JavaScript. Modules provide the possibility to group related logic, encapsulate it, structure your code and prevent pollution of the global namespace.

Method Overriding, in TypeScript, is a language feature that allows a derived class to provide a specific implementation of a method that is already provided by one of it’s or base classes. A member in a derived class is said to override a member in a base class when the derived class member has the same name and kind instance, or is static, as the base class member. A derived class will inherit all public members from its base class. The implementation in the derived class replaces the implementation in the base by providing a method that has the same signature, the same name or parameter and the same return type as the method in the base class.

The concept of classes is very similar to .NET/Java. A Class can have constructor, member variables, properties and methods. TypeScript also allows access modifiers “private” and “public” for member variables and functions.

The scope is set of objects, variables and function and the JavaScript can have global scope variable and local scope variable. There are three types of scope variable

Global Scope Variable: The global scope is a window object and it’s used out of function and within the functions.

Local Scope Variable: The local scope is a function object and it’s used within the functions.

Class Scope Variable: These variables are also called fields. Fields or class variables are declared within the class but outside the methods. These variables can be accessed using the object of the class. Fields can also be static. Static fields can be accessed using the class name.

The presence of a tsconfig.json file in a directory indicates that the directory is the root of a TypeScript project. The tsconfig.json file specifies the root files and the compiler options required to compile the project. And using this file, we can streamline building TypeScript project.

TypeScript can be installed and managed via npm, the Node.js package manager. To install TypeScript, first ensure the npm is installed properly. And then run the following command to install TypeScript globally on your system.

A typescript file is used to write more manageable and complex code in AppBuilder but before that, they need to be compiled to JavaScript. Here are the steps which are followed while compiling a typescript file to JavaScript: –

It should be firstly verified that the typescript engine has been enabled or not. In the title bar, click your user name and select options.

In the project navigator, select and right-click the TS files that are to be compiled.

Typing has always been about the variables the program. If I create a static typing language

I don’t have to immediately tell the compiler that this particular integer and will always be

an integer. It will be exactly what I stored in the program even If I forget while coding and changed its value by passing it to another class or something. A number of good language examples are C, C++, and Java. Dynamic typing, on the other hand, is the direct opposite of what the above is about. Ruby, Perl and of course our poster boy. JavaScript. This doesn’t mean anyone of these languages is inherently weak or bad. And that should be the focus.